The present invention relates to a method and a device for regenerating a particle filter built into an exhaust line of an internal combustion engine, particularly of the diesel type.
It relates in particular to a method and a device for regulating the heat release, or exotherm, of the particle filter.
In general, a particle filter is used to pick up particles and soot contained in the exhaust gases and prevent them from being released into the atmosphere. However, these particles and soots have the property of clogging the filter after a certain usage period and causing back-pressure to build up in the exhaust line, which may cause an engine malfunction.
It is known that as soon as this filter reaches a predetermined clogging level, a filter regeneration sequence is triggered, generally by the engine control. This regeneration sequence consists essentially of burning the particles and soots present in this filter. For this purpose, the temperature of the exhaust gases passing through the filter is raised temporarily to assist with combustion of these particles, this combustion generally being exothermic. The duration of this gas temperature rise depends on the increase in back-pressure of the gases in the exhaust line.
One method of raising this temperature consists of having the engine operate in lean mode, i.e. with richness less than 1, so that the oxygen present in the exhaust gases participates also in combustion of the particles and soots contained in the filter.
However, the combustion inside the filter cannot be controlled, which can lead to very high temperatures inside it. These temperatures can cause the material of which the filter is made to deteriorate or even be destroyed.
The problem is even more significant when other functions are built into this filter. In particular, the filter can be used as a substrate for catalysts such as platinum or rhodium to convert the gas pollutants present in the exhaust gases, such as carbon oxides (CO), unburned hydrocarbons (HC), or nitric oxides (NOx). In this configuration, when the catalyzed particle filter is regenerated, the internal exotherm of this filter is increased by catalytic conversion not only of the COs and HCs in the exhaust gases but also of the HCs that desorb from the internal structure of the particles and the COs resulting from combustion of these particles and soots. This has the drawback of causing deterioration of the catalytic phases present on this filter, which can no longer fulfill their function of converting the polluting gaseous phases present in the exhaust gases.
Document FR 2,829,526 teaches monitoring the temperature of the particle filter by a temperature sensor disposed in or downstream of this filter. When a temperature threshold is reached, the combustion of the particles and soots is limited or even stopped by reducing the concentration of the oxygen present in the exhaust gases passing through this filter.
Such an arrangement, although it is satisfactory, has the non-negligible drawback of not giving a true representation of the various temperatures prevailing in various regions of the filter, mainly when the temperature sensor is disposed downstream of the filter. When there is a local temperature elevation inside the filter, the sensor downstream of the filter cannot pick up such an increase and the regeneration continues, with the risk of locally degrading the filter. Also, the sensor inside the filter can pick up the temperature only in a very particular spot in the filter.